Coated hygroscopic salts



Patented Dec. 31, 1946 COATED HYGROSCOPIC SALTS Edgar Fajans, Blackley, Manchester, England, as-

signor to Imperial Chemical Industries Limited, a corporation of Great Britain No Drawing. Application April 13, 1944, Serial 4 Claims.

The present invention relates to the waterproofing of hygroscopic salts which are in the form of crystals, granules, etc., as obtainedin the course of manufacture.

The invention relates more especially to a treatment of ammonium nitrate, but is also applicable to other hygroscopic salts, for instance sodium nitrate, or crude common salt (sodium chloride).

The object of the invention is to render hygroscopic salts water-proof in the sense that their hygroscopicity is diminished to such an extent that the storage and operational difficulties ordinarily experienced with such salts are obviated or at least substantially reduced.

According to the invention hygroscopic salts in the form of crystals, granules, etc., as obtained in the course of manufacture are mixed with a spreading oil and a wax, in such proportions that there is enough spreading oil and Wax, together, to coat the surface of the particles of hygroscopic salt. The ratio of spreading oil to wax may vary .widely. The mixing may be carried out at room or higher temperature.

Thus, in carrying the invention into prac-' tical effect some or all of the ingredients may be heated, or conveniently the mixing may be done in a heated kettle. In this way the fluidity of the mixture of spreading oil and wax i increased, and the surface of the particles of hygroscopic salt is rapidly covered when the three ingredients are Worked together, by stirring or tumbling.

As spreading oils there may be used liquids of low volatilities, the molecules of which, or some of the molecules of which contain polar groups. Suitable liquids may contain oil-soluble polar compounds, e. g. barium oleate, vegetable oils or fatty acids preferably in a polymerised form and'a mineral oil of low volatility e. g. a lubricating oil. A suitable spreading oil is also obtained by subjecting hot lubricating oil to air oxidation until it has the required properties.

The invention is illustrated but not limited by the following examples in which the parts are by weight.

Example 1 0.8 part of oxidised spindle oil, prepared by passing air through grade 35 mineral lubricating oil at a temperature of 200 C. until the spreading pressure of the oil on Water exceeds 20 dynes per cm., and 0.2 part of paraflin wax (M. P. 50-55 C.) are heated to 70 C. To the hot solution of the wax in the oil, 100 parts of warm ammonium nitrate, technical crystals, are added.

The three ingredients are stirred together at 70 C. for minutes.-

In Great Britain December 2,

When 5 g. of this product is spread out in a thin layer in a Petri dish of 7.4 cm., diameter and exposed to an atmosphere of 100% relative humidity for 16 hours the increase in weight is less than 1%, while untreated ammonium nitrate similarly exposed increases in weight by 18%.

Example 2 Example 3 0.7 part of a 10% solution of a polymerised linseed oil fatty acid, itself prepared by heating the acid to 260 C. for 15 hours, in grade 35 lubricating oil and 0.5 part of parafiin wax with a melting point of 55 C. are heated to C.; to the molten mixture parts of ammonium nitrate in the form of crystals areadded and the ingredients are mixed together as described in Example 1.

The thus treated ammonium nitrate when tested by the method described in Example 1 increases in weight by about 0.5%.

I claim: 1. A process which comprises mixing a granular hygroscopic salt with a moisture-proofing agent consisting essentially of a spreading oil of low volatility having spreading pressure in excess of 20 dynes per centimeter, and parafiin wax, whereby the surface of the particles of the salt become coated with the said moisture proofing agent, said spreading oil having a mineral lubricating oil as its chief constituent and being a solution of barium oleate in the said mineral oil.

2. A process for moisture-proofing ammonium nitrate crystals which comprises mixing the said crystals with a moisture-proofing agent consisting of about 0.5 part by weight of a 10% solution of barium oleate in mineral lubricating oil, and about 05 part of paraffin.

3. The process set forth in claim 1 in which the 

